Asphalt, a useful material for paving and resurfacing roadways, may be modified by incorporation of rubber therein. See U.S. Pat. Nos. 3,891,585 and 4,069,182. Asphalt-rubber compositions are believed to be an improvement over asphalt alone, due to the increased flexibility, adhesivity, etc. However, due to the high viscosity, rubberized asphalt is difficult to apply by spraying. Therefore, it is known to heat asphalt and rubber blends to lower the viscosity and facilitate application. Heating requires special equipment and experienced personnel. Obviously, it is desirable to avoid working with a hot material at a job site; thus, asphalt and rubber blends have been modified by incorporation of various solvents therein to decrease the viscosity. For example, in U.S. Pat. No. 3,919,148, kerosene is taught as a useful solvent to decrease the viscosity of an asphalt-rubber blend. It is found that the volatility of kerosene caused a problem at the temperature at which the blend was applied. That is, if the kerosene-modified blend stood for too long, prior to application, the viscosity increased almost to the viscosity of a kerosene-free asphalt-rubber blend. Thus, less volatile oils may be used in place of the kerosene to lower the viscosity of the asphalt rubber blend. See U.S. Pat. Nos. 2,728,734, 4,021,393 and 4,068,023.
Another approach to providing a blend of asphalt and rubber in an easy applicable form may be found in a product comprising an emulsion of asphalt and rubber in water. Certain asphalt and rubber emulsions are pourable and sprayable at ambient conditions. Thus, the emulsion may be applied at the site, and as the emulsion breaks, the asphalt and rubber deposited therefrom is available as a paving material. Chip sealing applications using asphalt and rubber emulsions are now prevalent. Asphalt and rubber, however, are not easy to form into a stable emulsion. In U.S. Pat. No. 4,018,730 an asphalt pavement material is disclosed which is emulsified by a soap consisting essentially of water, an anionic water soluble emulsifying agent, a thickener and a halide of an alkali metal or an alkaline earth metal. Moreover, in the above-mentioned U.S. Pat. No. 4,021,393, it is disclosed that a asphalt-rubber-malthene paving composition may be emulsified using the emulsion system of U.S. Pat. No. 4,018,730. Other examples of emulsified blends of asphalt and rubber may be found in U.S. Pat. Nos. 3,785,852, 2,978,427, 3,565,842, 2,714,582 and 3,493,408. However, in many of the above references, the asphalt-rubber blend is prepared by mixing an asphalt emulsion and a rubber latex. Of course, in such emulsions as these, the asphalt and the rubber particles will exist separately, and thus a true rubberized asphalt is not obtained in either the emulsion state or upon application. See, in particular, U.S. Pat. Nos. 3,785,852 and 3,493,408.
In view of the obvious safety advantages, in working with water-continuous paving compositions, the advantages of asphalt-rubber emulsions are apparent. In view of this there is an on-going effort to continue to develop water-based asphalt and rubber emulsions which are stable and easily applied.